In order to check or monitor the functionality of exhaust gas aftertreatment systems used presently in motor vehicles, sensors are needed which make it possible to precisely ascertain the particle concentration present in a combustion exhaust gas. Furthermore, with the aid of such sensors, it should be possible to make a loading prognosis of, for example, a diesel particle filter provided in an exhaust gas system in order to achieve a high system reliability and thus be able to use more cost-effective filter materials.
A sensor for detecting particles in a fluid flow, which is designed based on a ceramic multilayer substrate is described in German Patent Application No. DE 10 2006 009 066. It includes two measuring electrodes spaced apart from one another, which are exposed to the combustion exhaust gas to be tested. If soot is deposited between the two measuring electrodes, a current flow occurs between the measuring electrodes when a direct voltage is applied to the measuring electrodes. A heating element of a layered design makes it possible to remove deposited soot particles from the electrodes or their surroundings thermally by burn-off and regenerate the sensor in this way.
After a successful regeneration, the next measuring phase is provided, in which soot is again deposited between the measuring electrodes.
If the temperature of the sensor element falls below a limiting temperature, for example, 100° C., during the measuring phase, water vapor may condense on the sensor element. Generally, the condensate adhering on and between the measuring electrodes renders the ongoing measurement unusable, making it necessary to interrupt this measuring phase. The sensor element must then first be regenerated by resetting it into the original state. Only after that may a new measuring phase begin.
This reduces the availability of the particle sensor signal pro rata temporis.